constructor in java defualt | constructor programs in java

Constructor in Java

Constructor is a block of codes similar to the method. It is called when an instance of the class is created. At the time of calling constructor, memory for the object is allocated in the memory.

It is a special type of method which is used to initialize the object.

Every time an object is created using the new() keyword, at least one constructor is called.

vIt calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.

There are two types of constructors in Java: no-arg constructor, and parameterized constructor.

Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.

Rules for creating Java constructor

There are two rules defined for the constructor.

1.    Constructor name must be the same as its class name

2.    A Constructor must have no explicit return type

3.    A Java constructor cannot be abstract, static, final, and synchronized

Types of Java constructors

There are two types of constructors in Java:

1.    Default constructor (no-arg constructor)

2.    Parameterized constructor

default constructor multiple constructor in java  

1.Java Default Constructor:

A constructor is called "Default Constructor" when it doesn't have any parameter.

Syntax of default constructor:

<class_name>{}

Example of default constructor

    //Java Program to create and call a default constructor  

    class Bike1{  

    //creating a default constructor  

    Bike1(){System.out.println("Bike is created");}  

    //main method  

    public static void main(String args[]){  

   //calling a default constructor  

   Bike1 b=new Bike1();  

}  

}  

    Output:

     Bike is created

2.    Java Parameterized Constructor:

A constructor which has a specific number of parameters is called a parameterized constructor.

Example of parameterized constructor

   //Java Program to demonstrate the use of the parameterized constructor.  

    class Student4{  

    int id;  

      String name;  

      //creating a parameterized constructor  

      Student4(int i,String n){  

      id = i;  

      name = n;  

     }  

     //method to display the values  

     void display(){System.out.println(id+" "+name);}  

   

      public static void main(String args[]){  

      //creating objects and passing values  

     Student4 s1 = new Student4(111,"Karan");  

     Student4 s2 = new Student4(222,"Aryan");  

     //calling method to display the values of object  

     s1.display();  

     s2.display();  

    }  

}  

      `Output:

    111 karan

    222 Aryan

Constructor Overloading in Java

In Java, a constructor is just like a method but without return type. It can also be overloaded like Java methods.

Constructor overloading in Java is a technique of having more than one constructor with different parameter lists. They are arranged in a way that each constructor performs a different task. They are differentiated by the compiler by the number of parameters in the list and their types.

Example of Constructor Overloading

    //Java program to overload constructors  

      class Student5{  

       int id;  

      String name;  

      int age;  

     //creating two arg constructor  

      Student5(int i,String n){  

      id = i;  

      name = n;  

     }  

    //creating three arg constructor  

     Student5(int i,String n,int a){  

     id = i;  

     name = n;  

     age=a;  

     }  

     void display(){System.out.println(id+" "+name+" "+age);}  

   

      public static void main(String args[]){  

      Student5 s1 = new Student5(111,"Karan");  

      Student5 s2 = new Student5(222,"Aryan",25);  

      s1.display();  

      s2.display();  

    }  

}  

   Output:

   111 karan 0

   222 Aryan 25

   

multiple constructoe exemple

   Java Copy Constructor

There is no copy constructor in Java. However, we can copy the values from one object to another like copy constructor in C++.

There are many ways to copy the values of one object into another in Java. They are:

• By constructor
• By assigning the values of one object into another
• By clone() method of Object class

            Example:

                                     //Java program to initialize the values from one object to another object.  

   class Student6{  

    int id;  

    String name;  

    //constructor to initialize integer and string  

      Student6(int i,String n){  

      id = i;  

      name = n;  

     }  

    //constructor to initialize another object  

    Student6(Student6 s){  

    id = s.id;  

    name =s.name;  

     }  

     void display(){System.out.println(id+" "+name);}  

   

     public static void main(String args[]){  

     Student6 s1 = new Student6(111,"Karan");  

     Student6 s2 = new Student6(s1);  

     s1.display();  

     s2.display();  

    }  

}  

    Output:

   111 karan

   222 Aryan